新手求助~（关于初级的神经网络问题）

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各位大虾，我在网上看到的教程里的一个程序段，本来想要试试看的：
7 T5 ~1 _4 k, z) I5 e, qnet=newff([-1 2; 0 5],[3,1],{'tansig','purelin'},'traingd');
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) f- N& o8 Q; S! p- X; Inet.trainParam.show = 50;
net.trainParam.lr = 0.05;
net.trainParam.epochs = 300;
- b( h  U, e, {1 [* Hnet.trainParam.goal = 1e-5;
p = [-1 -1 2 2;0 5 0 5];
7 `( l9 U1 j) K2 A! ~! bt = [-1 -1 1 1];


) `; D4 ?. g0 L  rnet=train(net,p,t);
TRAINGD, Epoch 0/300, MSE 1.59423/1e-05, Gradient 2.76799/1e-10

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7 Y# [" w$ ?' `* a$ r! O0 `TRAINGD, Epoch 50/300, MSE 0.00236382/1e-05, Gradient 0.0495292/1e-10
) L# X$ I) Q1 O3 VTRAINGD, Epoch 100/300, MSE 0.000435947/1e-05, Gradient 0.0161202/1e-10
TRAINGD, Epoch 150/300, MSE 8.68462e-05/1e-05, Gradient 0.00769588/1e-10
TRAINGD, Epoch 200/300, MSE 1.45042e-05/1e-05, Gradient 0.00325667/1e-10
- \$ h  K8 m9 M# yTRAINGD, Epoch 211/300, MSE 9.64816e-06/1e-05, Gradient 0.00266775/1e-10
TRAINGD, Performance goal met.
a = sim(net,p)
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2 y1 f* [3 O* X, Y" H( g/ kplot(p,t,p,a,'o')

% q3 {$ S; g0 B
但是为什么老是报错：
??? Input argument "net" is undefined.